Djokovic warned the rest of those contending for the title that he was playing as well as he ever has at the All England Club.

"I am really happy with the performance. I am playing some of the best tennis on grass of my career," he said.

"It was a very close match, it could have gone either way. He could have won the first two sets, he had a double break in the second.

"I don't know how I managed to go ahead, I don't know how I turned it around."

Seventh seed Berdych trailed Djokovic 13-2 in head-to-head encounters before the match but beat his rival at Wimbledon in 2010, in their only previous meeting on grass.

Analysis

For a set and a bit Tomas Berdych was absolutely brilliant but he made the fatal mistake of a terrible service game when he was up a double-break and let Novak Djokovic back into the match - and you simply can't do that.

The 27-year-old Czech pushed the world number one all the way in the first set, although he was unable to make too many dents in the formidable Djokovic serve.

An energised Djokovic, 26, hit 15 winners and only two unforced errors on the way to winning the opener, which he secured via a tie-break.

But Berdych broke to love early in the second set - only the third time Djokovic had been broken in the tournament - before forcing a double-break to go 3-0 ahead.

However, Berdych allowed his focus to slip in the next game and was broken back before Djokovic raised his levels again to level at 3-3.

And with Djokovic bristling again on Court One, Berdych fell apart when serving to stay in the set, handing it to his opponent with a tame forehand into the net.

It was the same story early in the third set, with Berdych sending down two double faults to give Djokovic a 3-1 lead, after which the steely Djokovic managed to keep him at arm's length.

Djokovic, winner of the men's singles at Wimbledon in 2011 and bidding for his seventh major title, has now reached 13 consecutive semi-finals at Grand Slam tournaments.

Eighth seed Del Potro looked like he might not last a game of his last-eight encounter against fourth seed Ferrer.

Media playback is not supported on this device

Del Potro shakes off injury to beat Ferrer

The Argentine fell heavily on his strapped left knee during the fifth point of the game, causing the match to be delayed for five minutes while he received treatment.

But the former US Open champion eased his way back into the match and saw his feisty opponent off in surprisingly straightforward fashion.

The 24-year-old Del Potro prevailed 6-2 6-4 7-6 (7-5) in two hours and 16 minutes to reach his first Wimbledon semi-final.

"It's going to be dangerous if I don't recover in the next few days," Del Potro said of his knee.

"I was really close to pulling out, I felt a lot of pain. But the doctor gave me some massive pills.

"I think I played my best tennis in this match, I'm so happy with my level at this moment."